1. Technical Field of the Invention
The invention relates generally to devices that include a man to machine interface (MMI) implemented using a touchscreen; and, more particularly, it relates to conductive patterns employed within such touchscreens.
2. Description of Related Art
Touchscreen technology is relatively new in the world of displays for stationary and mobile devices. Traditionally, an underlying layer of lines that can sense a user's touch are arranged in a patterned manner and are monitored iteratively for a signal that suggests a coordinate of a point that is touched. Initial systems were designed to detect a single touch. A new emphasis, however, is to develop touchscreen technology that can accurately detect multiple simultaneous touches.
Some current technology for multi-finger touch works by charging and discharging a voltage on a row or column of conductor and measuring the change in the charge when touched. This technology includes all stray capacitance in the measurement. One standard arrangement for the lines that detect touch is to use rows and columns of the sensing lines that include a series of diamond shaped areas connected end to end. The row and column lines are arranged so that the diamonds do not overlap each other, even if on different layers, and the rows and columns are placed so that they only overlap at the intersections of connection lines between the diamond shaped areas. The overlapping area of the intersection of the connection lines is kept very small to reduce capacitance and, therefore, the capacitive effects of the overlapped areas. The capacitive effects of the overlapped areas can be much larger than any other “noise” or “unusable signal” in the system.
The original touchscreen devices were small thereby resulting in the number of lines used for sensing touch being manageable given the iterative manner in which such lines are scanned. Traditionally, a cross point connection resulting from a touch resulted in a signal produced at a sensing line arranged horizontally would appear on a sensing line arranged vertically, or vice versa. Thus, if there were 10 horizontal lines (rows) and 10 vertical lines (columns), 100 possible points have to be scanned to determine whether a touch occurred. For a small screen, the diamond shaped areas could be made small so that a finger might touch more than one diamond at a time to assist in the accurate determination of the touch location.
As screens increase in size, however, the shaped areas for detecting touch tend to increase in size also to avoid or minimize an increase in a number of lines (vertical or horizontal) that must be monitored/scanned to detect a touch. For example, if a four inch monitor has twenty vertically arranged lines and 20 horizontally arranged lines, four hundred possible touch locations require monitoring on a repetitive basis (e.g., 50 times per second) for a cross point monitoring scheme. It is easy to see that if the screen size increases to a 12 square inch area, and the arrangement of the lines and size of the shaped areas remains constant, the number of possible touch locations increases to 3600. If the scan rate is 50 times per second, 2000 scan points are performed per second for a 4″ touchscreen, and 18,000 scan points are performed per second for the 12″ touchscreen. Accordingly, designers have tended to increase, perhaps proportionally, the size of the shaped areas to match the increase in screen size so as to not increase the number of possible touch locations that require monitoring.